It's just coincidence that the clutch is gone after the master cylinder. Do you know if the clutch was replaced when the engine was installed? It could be 150000kms old for all you know.
Ring ABS or Repco and get some prices. You will need a full clutch kit.
Make sure you know the model of the car that the engine came out of and the year it was manufactured.
It should be only a few hundred for parts.
You can DIY if you know how to pull out a tranny. The main thing you might have trouble with is aligning the clutch upon reassembly. It's pretty cheap and easy to find a clutch aligning tool. Don't try without one as it can make life very difficult if it isn't properly aligned.
It's not a hard job, just time consuming and fiddly to do on the ground. The bigger the transmission the harder the job.
Good luck!

so there is no noteable fluid drop when pressing pedal so that is good. starting to get some slippage in 2nd and 3rd now.

is it just coincidence that the clutch has gone after the master was replaced? so how do i id. a replacement? will it be readily sourced? is it likely to be just the plate? and can i diy this?

what's toe clearance?

You're right Don, it does.
My bad.

I had a similar issue with my celica 5 speed behind an A-series although cable clutch. Pedal take up point came out further and further but still was not slipping. Adjusted the cable lasted a day or to before it pretty much let go all together. Slipping badly. Pulled it out to find the diaphram buggered.

Actually shoota, as the clutch wears, the diaphragm moves further away from the flywheel as it wears,

Also, the fluid should not really move much at all when the pedal is depressed, nothing noticeably anyway.

As for the symptons, sounds like a naturally worn out clutch. High release and slippage point to a friction plate that has little material left or that it may have a pressure plate that has not enough clamping force. Perhaps the wrong pressure plate was used to start with.

how much toe clearance do u have jason ? , that is all u can adjust on a hydraulic system

if the pedal doesn't engage until right at the top & u have slippage in 4th gear , well those symptoms to me reading it over the internet without driving the car tell me the clutch is #OOPS#ed mate.

The fluid won't drop much when you push the pedal down. As the piston moves forward in the bore it covers the hole that goes to the reservoir. It might fluctuate a tiny bit but not much.
If it looks like the clutch fork is trvelling it's full travel forwards AND back then it's looking more and more like a clutch plate issue.

Yes, that's right. It should not rise when the pedal is depressed.

Many hydraulic clutch setups have minimal adjustment.

But the Datsun 1200 has full adjustment:
* Adjustable Pedal travel
* Adjustable master cylinder rod
* Adjustable slave cylinder

So you cannot always go by common wisdom. Datsun 1200 LHD uses a hydraulic clutch setup.

had a look under there this arvo as my son pressed the pedal - nothing untoward. so, if you look into the resevoir as the pedal is depressed you should see a notable drop in the fluid level? and the fluid should return on release.

The fluid level should drop. As the clutch plate wears the slave cylinder moves further forward in its bore. this obviously creates a cavity behind it that needs to be replaced by fluid, hence lowering the level.
Get under the car and get someone to activate the pedal. You may be able to see something funny while you're under there.
Also check the rubber boot that the clutch fork goes through into the box, just to make sure it isn't jamming the clutch forks travel.
If all that looks ok, if the clutch slave is easily accessible, whip it off and pull it apart just to confirm everything is ok. There's a possibility that the piston could be stuck in the bore, holding pressure on.
While the slave is out and the fork boot off, see if you can use a folding telescopic mirror and torch (shine torch onto mirror to reflect into the box) to see if you can see the clutch diaphragm fingers.
Other than that, without being there, I can't think of anything else!